Generally, when transmitting signals through radio communication, sometimes so-called fading occurs in which receiving magnitude changes within a short period of time due to a fluctuation in the propagation medium through a change in propagation mode or electric wave path.
In a conventional type of radio communication apparatus, for instance, when transmitting an SSB audio signal and a data signal for controlling a system in a narrow band having a bandwidth of 5 kHz, fluctuation of amplitude due to frequency coherence as well as fading due to mobile communication is corrected by inserting a pilot signal.
In the conventional type of radio communication as described above, however, an additional bandwidth for protecting the pilot signal is required, and when transmitting an SSB audio signal and a system control data signal in a narrow band, the bandwidth for an audio signal is limited, which makes it impossible to improve quality of voice as well as to execute high speed transmission.